1. Field of the Invention
This invention relates to polyurethane elastomer gels which are filled with dispersed discrete droplets of aqueous liquids and to a method of making such filled gels.
2. Description of the Prior Art
Polyurethane elastomers are fabricated from the reaction of polyisocyanates and polyols. The encapsulation of non-aqueous liquids in polyurethane films and elastomers is described in U.S. Pat. No. 3,872,050. In general, when attempts are made to encapsulate aqueous liquids in polyurethane, the water functions as a blowing agent and creates polyurethane foams which are undesirable in the encapsulated gel products.
Japan Pat. No. 49-14155 (1974) describes a water filled polyurethane gel which contains a large amount of water as a filler in homogeneous dispersion. The use of large quantities of water avoids the objectionable formation of foams when water is contacted with polyisocyanates prepolymers as described in that Japan patent. The difficulty with water filled polyurethane elastomer gels is several fold. First, such water filled polyurethane elastomer gels tend to shrink rapidly by loss of the water. The shrunken gel can be partially revived by soaking in water or aqueous fluids. However the dimensional recovery is less than 90 percent.
Secondly, the water filled polyurethane elastomer gels do not develop tackiness on the surface. Surface tackiness is a desirable characteristic for many end use applications of such liquid filled polyurethane elastomer gels. In addition the processing time for handling water filled polyurethane elastomer gels is limited, perhaps 60 seconds maximum.
Thus there is a need for a liquid filled elastomer gel which has substantially retarded shrinking tendencies, which can develop surface tackiness where desired, and which has an extended processing time to facilitate preparation of useful products.